Field of the Invention
The present invention relates to wireless communication and, more particularly, to a device to device (D2D) communication method performed by user equipment in a wireless communication system and user equipment supporting the same.
Related Art
In International Telecommunication Union Radio communication sector (ITU-R), a standardization task for International Mobile Telecommunication (IMT)-Advanced, that is, the next-generation mobile communication system since the third generation, is in progress. IMT-Advanced sets its goal to support Internet Protocol (IP)-based multimedia services at a data transfer rate of 1 Gbps in the stop and slow-speed moving state and of 100 Mbps in the fast-speed moving state.
For example, 3rd Generation Partnership Project (3GPP) is a system standard to satisfy the requirements of IMT-Advanced and is preparing for LTE-Advanced improved from Long Term Evolution (LTE) based on Orthogonal Frequency Division Multiple Access (OFDMA)/Single Carrier-Frequency Division Multiple Access (SC-FDMA) transmission schemes. LTE-Advanced is one of strong candidates for IMT-Advanced.
There is a growing interest in a Device-to-Device (D22) technology in which devices perform direct communication. In particular, D2D has been in the spotlight as a communication technology for a public safety network. A commercial communication network is rapidly changing to LTE, but the current public safety network is basically based on the 2G technology in terms of a collision problem with existing communication standards and a cost. Such a technology gap and a need for improved services are leading to efforts to improve the public safety network.
The public safety network has higher service requirements (reliability and security) than the commercial communication network. In particular, if coverage of cellular communication is not affected or available, the public safety network also requires direct communication between devices, that is, D2D communication.
D2D communication may have various advantages in that it is communication between devices in proximity. For example, D2D UE has a high transfer rate and a low delay and may perform data communication. Furthermore, in D2D communication, traffic concentrated on a base station can be distributed. If D2D UE plays the role of a relay, it may also play the role of extending coverage of a base station.
Meanwhile, one of important procedures when D2D communication is performed is to discover another device in proximity. To this end, D2D UE sends a discovery request signal (it may be hereinafter called a discovery request signal), and another D2D UE may send a discovery response signal in response to the discovery request signal. Furthermore, in D2D communication, direct communication is performed between two types of UE.
Meanwhile, a collision between a D2D signal used in D2D communication and another signal may be generated in UE attempting to perform D2D communication. If UE sends a D2D signal without affecting transmission quality of another signal or requirements, the UE may send a D2D signal and another signal at the same time.
However, practically, although a D2D signal and another signal are transmitted in different frequency bands, they inevitably affect each other. Accordingly, if a point of time at which a D2D signal is transmitted collides against a point of time at which another signal is transmitted, there is a need for a D2D communication method and device in which how the collision will be handled is taken into consideration.